Can we still say we are gambling if the event is something we are at least 90% sure that we are going to win?
The result is not 100% guaranteed so it is still gambling. As long as you put your luck on is considered gambling for me. Anything can happen in gambling, and that 10% chance to lose is still possible if you get unlucky.
It's best to not bet big amount just because you feel confident. If you do bet huge amount then lose, it might make you to gamble more wanting to recover that loss.